The present invention relates to drive and control systems for lifting gates, in particular for high-speed industrial lifting gates as well as a lifting gate with such a drive and control system.
Lifting gates are in prior art known for example from DE 40 15 214 A1 in which a lifting gate is disclosed with slatted armor and an electric drive motor. This lifting gate comprises two guide tracks which are arranged on the two opposite sides of the gate opening, and slatted armor with slats that are mounted on hinge straps spaced from each other in such a manner that the hinge pins engage within a space between the adjacent slats. It is further disclosed that the lifting gate is formed as an industrial lifting gate within the meaning of a high-speed gate. Such lifting gates are designed as rolling gates or spiral gates that close or open walk-in or drive-in gate openings.
For gates that need to have the gate leaf moved vertically for opening the drive-through or walk-through passage, there is the danger that it cannot be excluded in the event of failure of a servo or actuating member that the gate leaf crashes down in an uncontrolled and hazardous manner due to the gravity load on the gate leaf. These dangers are greater the faster the gate leaf is moved during regular operation. In so-called high-speed gates, gate leaf speeds of up to 4 m/s can be reached, whereas the gate leaves with conventional industrial lifting gates are moved at speeds of typically 0.2-0.3 m/s.
Elaborate measures are taken to minimize the hazard posed by these gates.
A common measure is to balance the weight of the gate leaf by counterweights or weight counterbalancing springs, in order to create a balancing system that is ideally configured such that the gate leaf is balanced in every position of the gate leaf by the balancing system, thereby avoiding hazardous lag.
Practice shows that this can not be realized in the way in that balancing can not be given uniformly at all positions of the gate leaf and not for the entire service life. With tension springs, for example, the spring characteristic changes over time so that the balancing moment required can not be guaranteed in the long run.
Also crashing devices based on centrifugal actuation are known that respond to an increase in the lowering speed of the gate leaf. Centrifugal actuation, however, responds only relatively slowly and can therefore be used only for low closing speeds. At higher closing speeds, the lag distance of the gate leaf would be hazardous and the load on the mechanical components would be relatively high.
The same applies to so-called transmission breakage protection devices that are constructed such that, upon loss of power transmission between the individual gear elements, holding jaws engages with the main gear of the transmission.
With conventional lifting gates, asynchronous motors are employed with worm, bevel, and spur gear transmissions and in combination with mechanical brakes. Transmissions and brakes are subject to permanent wear. Stresses arise not only from normal operation of the gate systems, but most of all also from the measures initiated in case of danger, such as safety reversal or an emergency stop. Safety reversals triggered by safety sensors, such as shut-off bars or light barriers, must within the shortest possible time cause the gate leaf to come to a standstill with subsequent reversal of the gate leaf direction in order to limit contact forces upon human body parts. Emergency stop processes lead to a stop in the shortest time. Power failures lead to an instantaneous emergency stop.
As explained above, power failure is for the conventional design of the gates the situation which puts the highest loads on the transmission of the gate drive and the holding brake. The drive power is in an instant no longer present, the brake operated in the closed-circuit principle is actuated instantaneously and must not only absorb gravitational forces but also the kinetic energy of the gate leaf mass. The loads on gears and shafts as well as other parts of the support system increase at a square function of the closing speed.
Brakes commonly being attached to the motor shaft ensure that the gate leaf is held in position after the drive is switched off. These brakes operated in a closed-circuit principle are subjected to high loads, in particular in the event of power failure, because they have to absorb the kinetic energy of the gate leaf weight instantaneously and in an uncontrolled manner. The design complexity of such safety-related mechanical brakes that can also make power failure manageable is correspondingly high.
In addition, the braking effect of such brakes is dependent on several factors, such as the operating temperature or possible fouling. Typically, the braking effect of the brakes abruptly decreases at about 150° C. Any fouling of the brake discs with oily substances also reduces the braking effect dramatically.
The adjusting range of asynchronous motors, i.e. the ratio of the rated rotational speed and the lowest rotational speed at which the drive can still maintain the nominal speed is limited. The required moment of force is therefore at low rotational speeds not available and also the reaction time of the brake is to be considered, so that the brakes must be activated already prior to the standstill. The kinetic energy to be absorbed by the brake arising there leads to great wear.
Due to these stresses, the brakes are to be tested at least annually and in dependence of the number of actuations. Safety experts recommend to unconditionally replace brakes at the latest after 2,000 full load actuations caused by emergency stop actuations or power failures.
In order to enable the gate to be opened also after power failure, the electromechanical holding brakes employed are equipped with manually operated elements such as cable winches, cranks or manual chains which cancel the effect of the holding brake when used. The gate leaf thereby is either raised by the weight counterbalancing device, can be pushed up, or be rolled upwardly by operating a crank or a hand chain.
In general, the asynchronous motors are operated on gates by use of frequency converters enabling the most uniform acceleration of the gate leaf. During the downward motion induced by gravity or during reversal operations of the gate leaf, the motor is in a generator mode. Frequency converters usually require a so-called braking resistor in which this regenerative energy is depleted, i.e. is converted into heat energy.
The object of the present invention is to overcome these disadvantages and to provide an improved drive and control system for lifting gates in order to reduce the crash risk and the stresses on gears, shafts, brakes and weight counterbalancing devices.
This is satisfied by the features of the independent claim. Advantageous embodiments are the object of the dependent claims. It is the particular approach of the present invention to replace the asynchronous motor with an attached brake conventionally used as a drive with a motor, which with the use of appropriate control and regulating devices is able to decelerate the gate leaf of the lifting gate in a motor-driven manner to zero speed and hold it at a standstill in this position.
According to a first aspect of the present invention, a drive system is provided for a lifting gate with a vertically movable gate leaf. The drive system comprises a drive motor connectable to the gate leaf which is adapted to move the gate leaf vertically and a control system for actuating the drive motor. The drive system is characterized in that the drive motor can be down-regulated up to zero rotational speed and the control unit is upon the occurrence of a stop condition adapted to actuate the drive motor such that its rotational speed is reduced in a controlled manner and the gate leaf is thereby braked in a motor-driven manner, where the drive motor is configured to provide sufficient torque at zero rotational speed to hold the gate leaf at a current position, and the control system is configured to ensure this also during power failure.
According to a second aspect of the present invention, a lifting gate is provided with a vertically movable gate leaf and a drive system according to the first aspect of the invention.
The drive motor can advantageously be coupled to the gate leaf directly, in particular without gearing. This reduces structurally complex gearing units prone to wear and defect.
The drive motor can advantageously be formed as a synchronous motor. Synchronous motors are characterized as being highly regulatable and robust. They deliver high torques at small dimensions so that they can optionally be configured without transmission gearings such that their torque is sufficient for customary gate leaf weights.
In addition, synchronous motors, in contrast to conventional asynchronous motors, can be operated in current regulating mode, so that controlled operation is given up to zero rotational speed and even when stalled (zero rotational speed), sufficiently high torque can be generated to hold the gate leaf at a standstill against the force of gravity.
In a further favorable embodiment, the drive system further comprises an electrical energy storage, preferably in the form of an accumulator unit that is adapted to supply the drive motor and the control unit with electrical energy in case of power failure. Advantageously, the control unit can there be configured to detect power failure and to interpret this as an emergency condition so that the drive motor is in the event of power failure capable to reduce the speed and hold the gate leaf at a standstill. Weight-counterbalancing the gate leaf can in this manner also be dispensed with.
The synchronous drive can optionally be configured such that it can move the gate leaf even without the use of weight counterbalancing systems. At the same time, the power regulation of the synchronous drive can recuperate the freed energy released during braking and/or when closing the gate, for example, in a rechargeable accumulator unit or a capacitor unit. The design complexity associated with the weight counterbalancing systems can therefore also be reduced without increasing the load on mechanical supports or compromising safety.
In addition, the control unit can further be adapted to enable an emergency operation of the lifting gate in the event of power failure, in particular actuate the drive motor for an emergency opening of the lifting gate. The electrical energy storage thereby enables an emergency operation.
The drive system can advantageous further comprise a power regulating unit for actuating the drive motor, where the power regulating unit is adapted to recuperate the electrical energy generated during motor-driven deceleration of the gate and to charge the electrical energy storage with the recuperated energy. In this way, driving the lifting gate can be effected in an extremely energy-efficient manner, a characteristic that can be of importance in particular during accumulator-based emergency operations.
The control unit can advantageously further be adapted to determine an actual value on the basis of a signal supplied by the position sensor indicating a position or position change of the lifting gate, and to actuate the drive motor based on a comparison of the actual value with a reference value. It is in this manner possible to enable precise regulation of the gate motion. Based on a comparison of a reference value to an actual value, a reaction can in the event of deviation occur in the form of a motion interruption.
In a further advantageous embodiment, the control unit can monitor the residual accumulator charge and, when a predetermined lower threshold is reached, drive the gate leaf into a secure and crash-safe position with the remainder of the energy. A further accumulator unit, provided as a redundant protection, can provide this energy. In an alternative embodiment, a mechanical brake can assume the function of this redundant protection. In the event that the gate leaf remains in the stop position for a long time, the brake can for reasons of energy savings be switched to be activated.
It can by use of position sensor readings be verified whether the holding position is maintained in a stable manner. If it is determined that the holding position is not maintained, then the drive motor is again energized for bringing about renewed holding at zero rotational speed or driving to a secure crash-safe position. In this case, a warning to inspect and repair the brakes can also be outputted.